EP4650560A1 - Thread profile with tilted roots - Google Patents

Abstract

A percussive drill component (2) having a longitudinal central axis (14) comprising at least one threaded part (4); wherein threaded part comprises a plurality of thread profiles (16); wherein each thread profile includes a crest (6), a root (8), a contact flank (10); and a non-contact flank (12) and wherein the root in each of the thread profiles is inclined relative to the longitudinal central axis.

Description

Field of invention
• The present disclosure generally relates to a thread profile for stronger connections, fewer abrupt failures and reduced stress for use in percussion drilling.
Background art
• Percussion drilling is used to create a long borehole via a plurality of elongate drill string rods coupled together end-to-end by interconnected male and female threads. The well-established technique breaks rock by hammering impacts transferred from the rock drill bit, mounted at one end of the drill string, to the rock at the bottom of the borehole. Typically, the energy required to break the rock is generated by a hydraulically driven piston that contacts the end of the drill string (via a shank adaptor) to create a stress (or shock) wave that propagates through the drill string and ultimately to the base rock level.
• Percussive drilling components are typically coupled together via threaded parts. Generation of stress in the roots of the thread causes wear to the threaded parts and premature failure of the couplings. One option to reduce stress in the thread would be to increase the contact flank radii, however the problem with this solution is that to compensate for this, either the distance between the contact flank radii and the non-contact flank radii has to be reduced and / or the non-contact flank radii has to be reduced, therefore the stress levels in other regions of the thread root would increase and no benefit would be gained.
• Therefore, the problem to be solved is how to reduce and balance out stress levels in the root of the thread.
Summary of the Invention
• It is an objective of the present invention to provide a percussive drill component having a longitudinal central axis and comprising at least one threaded part; wherein the threaded part comprises a plurality of thread profiles; wherein each thread profile includes a crest, a root; a contact flank; a non-contact flank; a contact flank transition section between the root and the contact flank; and a non-contact flank transition section between the root and the non-contact flank; wherein the root in each of the thread profile is inclined relative to the longitudinal central axis.
• Advantageously, by tilting the root of the thread it is possible to enlarge the radii in the contact flank transition section which will reduce stress levels in the root of the thread without increasing stress levels at the non-contact flank transition section. By tilting the root of the thread, the cross-sectional area between the thread and longitudinal central axis is increased, the increased volume of steel present reduces the level of stress and makes the thread stronger in the non-contact radii, thus making it possible to reduce the radii to the non-contact flank without increasing stress in this region. Furthermore, the small radii to the non-contact flank is advantageous for aiding unthreading. Consequently, the overall level of stress in the thread is reduced making it less prone to wear and premature breakage and thus the lifetime of the threaded coupling is increased.
• In one example embodiment the roots comprise a straight section. This is advantageous for simplifying the manufacturing process.
• In some example embodiments there is an angle (α) between the longitudinal axis and the root wherein α is between 0.1 - 20°. Advantageously, this angle range provides the optimal balance between stress reduction and wear volume in the thread profile.
• In some example embodiments the contact flank transition section has a contact flank radius (r₁) and the non-contact flank transition section has a non-contact radius (r₂) and wherein r₁>r₂. Advantageously, this reduces stress in the root of the thread and aids unthreading.
• In some example embodiments r₁ is between 1.0 - 8.0 mm. Advantageously, this reduces stress levels.
• In some example embodiments r₂ is between 1.0 - 8.0 mm. Advantageously, this reduces stress levels.
• In some example embodiments at least one of the contact flank transition section and the non-contact flank transition section has a curvature defined by a portion of an ellipse having a semi-major axis (a); a semi-minor axis (b); and an exponential factor (n) according to the equation: $${\left|\frac{x}{a}\right|}^n+{\left|\frac{y}{b}\right|}^n=1$$ wherein n is between 1.1 - 4. Advantageously, this reduces stress levels in the thread profile.
• In some example embodiments the semi-major axis (a) and the semi-minor axis (b) are non-parallel relative to the longitudinal central axis. Advantageously, this enables the largest possible curvature to be positioned in the region of the transition section(s) having the smallest cross section. Consequently, less steel needs to be removed to form the threaded profile without needing to change the length of the flank, therefore the overall stress level in the threaded part is reduced making it less prone to wear or premature breakage and thus the lifetime of the threaded coupling is increased.
• In some example embodiments there is a contact flank angle (β) between the root and the contact flank and wherein β is between 115 - 165°. This range is advantageous for coupling and uncoupling of the threaded parts.
• In some example embodiments there is a non-contact flank angle (γ) between the root and the non-contact flank and wherein γ is between 115 - 165°. This range is advantageous for coupling and uncoupling of the threaded parts.
• In some example embodiments on each thread profile the contact flank transition section has a first axially innermost end and the non-contact flank transition section has a second axially innermost end; a first length (L₁) is measured between the first axially innermost end and the longitudinal central axis; a second length (L₂) is measured between the second axially innermost end and the longitudinal central axis; wherein within in the same thread profile L₂>L₁. Advantageously, the cross-sectional area, i.e., the volume of steel, in the non-contact flank is increased which compensates for any stress increase caused by reducing the non-contact flank radii to be able to accommodate an increase in the contact flank radii. Thus, overall providing a thread form having reduced stress.
• In some example embodiments the crests and roots of the thread profiles are cambered along the length of the threaded part. Advantageously, this improves the stiffness of the coupling when subjected to bending loads. The cambered threads distribute the bending load more evenly across the length due to the curvature thereof aligning better with a curvature of the bending. Furthermore, coupling and uncoupling times are reduced.
Brief description of drawings
• A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:
• Figure 1 is a schematic drawing of a drilling component.
• Figure 2 is a schematic drawing of the thread profile showing the tilted root.
• Figure 3 is a schematic drawing of a thread profile showing the tilted thread root illustrating α.
• Figure 4 is a schematic drawing of a thread profile showing a tilted elliptical transition section.
• Figure 5 is a schematic drawing of a thread profiles howing the tilted thread root illustrating β and γ.
Detailed description
• Figure 1 shows a percussive drill component 2 having a longitudinal central axis 14 comprising at least one threaded part 4. There are typically three or more thread profiles on the threaded part 4. The threaded part 4 could be male or female. The component 2 may have one male threaded part; or one female threaded part; or two male threaded parts; or two female threaded parts; or one male threaded part and one female threaded part. The threaded part(s) 4 may have any suitable thread form, for example but not limited to trapezoidal. The threaded part(s) could be a single, double or triple thread form. The percussive drilling component could for example be, but not limited to, a rod, tube, shank adapter, drill bit, thread adapter or coupling sleeve. The drill component 2 could be configured for either a shoulder contact or bottom contact coupling.
• Figure 2 shows a schematic drawing of a thread profile of the threaded part(s) 4. The threaded part(s) 4 comprises a plurality of thread profiles 16; wherein each thread profile 16 includes a crest 6 (otherwise known as a thread top), a root 8 (otherwise known as a thread bottom), a contact flank 10; a non-contact flank 12; a contact flank transition section 22 between the root 8 and the contact flank 10 and a non-contact flank transition section 24 between the root 8 and the non-contact flank 12. The crests may have any suitable form, for example flat, curved, straight or inclined. Typically, the contact flanks 10 and the non-contact flanks 12 are straight. The root 8 in each of the thread profile 16 is inclined relative to the longitudinal central axis 14. In other words, the root 8 of each thread profile 16 is non-parallel with the longitudinal central axis 14. A single thread profile 16 is defined as being from the mid-point of one crest 6 to the mid-point of the adjacent crest 6.
• In some example embodiments the roots 8 comprise a straight section. In other words, the roots 8 of the threads profiles 16 are not curved.
• Figure 3 schematic drawing of single thread profile (not to scale) showing there is an angle (α) between the longitudinal axis 14 and the root 8. In some example embodiments α is between 0.1 - 20°. For example, α is between 1 - 15°, for example α is between 2 - 10°.
• Figure 3 also shows that contact flank transition section 22 has a contact flank radius (r1), and the non-contact flank transition section 24 has a non-contact radius (r2). In some example embodiments r₁>r₂.
• In some example embodiments r₁ is between 1.0 - 8.0 mm, for example between 1.5 - 5.0 mm, for example between 2.0 - 4.0 mm.
• In some example embodiments r₂ is between 1.0 - 8.0 mm, for example between 1.5 - 5.0 mm, for example between 2.0 - 4.0 mm.
• In some example embodiments at least one of the contact flank transition section 22 and the non-contact flank transition section 24 has a curvature defined by a portion of an ellipse having a semi-major axis (a); a semi-minor axis (b) and an exponential factor (n) according to the equation: $${\left|\frac{x}{a}\right|}^n+{\left|\frac{y}{b}\right|}^n=1$$ wherein n is between 1.1 - 8. For example, n is between 1.5 - 4. For example, n is between 1.5 - 2.5 For example, n is 2.
• Figure 4 an enlargement of a single thread profile (not to scale) shows that in some example embodiments the semi-major axis (a) and the semi-minor axis (b) are non-parallel relative to the longitudinal central axis 14.
• The contact flank transition section 22 and the non-contact flank transition section could alternatively have any other suitable curvature.
• Figure 5 shows that is an enlargement of a single thread profile (not to scale) showing that there is a contact flank angle (β) between the root 8 and the contact flank 10 and wherein there is a non-contact flank angle (γ) between the root 8 and the non-contact flank 12. In some example embodiments β is between 115 - 165°, for example β is between 122.5°-157.5°, for example β is between 135°-150°. In some example embodiments γ is between 115 - 165°, for example γ is between 122.5°-157.5°, for example γ is between 135°-150°.
• Figure 3 also shows that on each thread profile 16 the contact flank transition section 22 has a first axially innermost end 18 and the non-contact flank transition section 24 has a second axially innermost end 20; a first length (L₁) is measured between the first axially innermost end 18 and the longitudinal central axis 14; a second length (L₂) is measured between the second axially innermost end 20 and the longitudinal central axis 14 and wherein within in the same thread profile 16 L₂>L₁. The axially innermost ends 18, 20 are considered to be where the curvature of the transition sections 22, 24 end and the start of the root 8 begins.
• In some embodiments the crests 6 and roots 8 of the thread profiles 16 are cambered along the length of the threaded part 4. If the thread is cambered L₁ and L₂ will be vary for different thread profiles 16. If the thread is not cambered L₁ will be the same for all thread profiles and L₂ will be the same for all thread profiles. Further details of cambered thread profiles are described in EP 3536894 .
• References in the description to "one embodiment," "an embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature or a particular combination of features (e.g., component(s), element(s), integer(s), structure(s), operation(s), and/or step(s)), but every embodiment may not necessarily include the particular feature or the particular combination of features. Such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, or a particular combination of features, is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, or combination of features, in connection with other embodiments whether or not explicitly described.

Claims (12)

1. A percussive drill component (2) having a longitudinal central axis (14) comprising at least one threaded part (4);

   wherein threaded part (4) comprises a plurality of thread profiles (16);

   wherein each thread profile (16) includes a crest (6), a root (8), a contact flank (10); a non-contact flank (12); a contact flank transition section (22) between the root (8) and the contact flank (10); and a non-contact flank transition section (24) between the root (8) and the non-contact flank (12);

   characterised in that:
   the root (8) in each of the thread profile (16) is inclined relative to the longitudinal central axis (14).
2. The component (2) according to claim 1 wherein the roots (8) comprise a straight section.
3. The component (2) according to any of the previous claims wherein there is an angle (α) between the longitudinal axis (14) and the root (8) and wherein α is between 0.1 - 20°.
4. The component (2) according to any of the previous claims wherein the contact flank transition section (22) has a contact flank radius (r₁) and the non-contact flank transition section (24) has a non-contact radius (r₂) and wherein r₁>r₂.
5. The component (2) according claim 4 wherein r₁ is between 1.0 - 8.0 mm.
6. The component (2) according to claim 4 or claim 5 wherein r₂ is between 1.0 - 8.0 mm.
7. The component (2) according to any of claims 1-3 wherein at least one of the contact flank transition section (22) and the non-contact flank transition section (24) has a curvature defined by a portion of an ellipse having a semi-major axis (a);
   a semi-minor axis (b) and an exponential factor (n) according to the equation: $${\left|\frac{x}{a}\right|}^n+{\left|\frac{y}{b}\right|}^n=1$$ wherein n is between 1.1 - 8.
8. The component (2) according to claim 7 wherein the semi-major axis (a) and the semi-minor axis (b) are non-parallel relative to the longitudinal central axis (14).
9. The component (2) according to any of the previous claims wherein there is a contact flank angle (β) between the root (8) and the contact flank (10) and wherein β is between 115 - 165°.
10. The component (2) according to any of the previous claims wherein there is a non-contact flank angle (γ) between the root (8) and the non-contact flank (12) and wherein γ is between 115 - 165°.
11. The component (2) according to any of the previous claims wherein on each thread profile (16) the contact flank transition section (22) has a first axially innermost end (18) and the non-contact flank transition section (24) has a second axially innermost end (20); a first length (L₁) is measured between the first axially innermost end (18) and the longitudinal central axis (14); a second length (L₂) is measured between the second axially innermost end (20) and the longitudinal central axis (14); wherein within in the same thread profile (16) and L₂>L₁.
12. The component (2) according to any of the previous claims wherein the crests (6) and roots (8) of the thread profiles (16) are cambered along the length of the threaded part (4).